Gases affecting the global warming are called greenhouse games and such greenhouse gases include carbon dioxide, methane, CFC and so on. According to the announcements reported in 2010, an emission amount of carbon dioxide over the world was about 33 billion tons, which was an increase of about 45% over the emission amount in 1990, and Korea ranked the 7th in the world in the emission amount of carbon dioxide and the 3rd in the increase rate of the amount. Foreign advanced countries have already led to reduce the emission amount of carbon dioxide by introducing the emission trading system or the carbon tax system.
With respect to methods for reducing the emission amount of carbon dioxide, there are generally capture, storage and conversion processes. Carbon dioxide capture and storage (CCS) technology isolates carbon dioxide discharged from big emission sources such as power, steel, and cement plants and so on from the air, and is a core technology occupying from 70% to 80% of whole expenses. Captured carbon dioxide may be stored in the ocean, under the ground, on the ground surface and others, but the storage in the ocean may cause a problem in the marine ecosystem, and the storage on the ground surface is still at the initial technology stage due to problems in storing places and others. Further, in view of transportation of captured carbon dioxide, there is a difficulty in widely commercializing the technology. In light of the foregoing, the process for conversion of carbon dioxide holds a prevailing position in both environmental and economic aspects, and can resolve the aforementioned problems, especially, through an electrochemical conversion method.
Conversion of carbon dioxide using electric energy can convert carbon monoxide, formic acid, methanol, methane and others into various organic compounds by reacting them through an electrode reaction under a condition of a room temperature and an atmospheric pressure depending on types of electrode materials and reaction conditions. In an electrochemical conversion method, since potential differences of reduction of carbon dioxide and generation of hydrogen in an aqueous solution are significantly close to each other, the reduction of carbon dioxide is interrupted by the competition of the two reactions. Accordingly, it is necessary to use an electrode having a large overpotential to the generation of hydrogen and a catalyst or an electrode surface for selectively converting only carbon dioxide.
In recent, researchers have actively studied for formic acid, and the formic acid is used to keep foods necessary for livestock breeding fresh and also used in a small amount as a preservative for foods. Besides, formic acid may be used as a fuel of a formic acid fuel cell, and the current price of formic acid to input energy is the highest in other materials that can be subject to be converted. Formic acid is disadvantageous in that, despite the tendency for the price of formic acid to have increased each year, uses of formic acid are still a few. Recently, many researches on a method that produces formic acid by electrolyzing carbon dioxide have been conducted (Korean Patent No. 10-468049).